Tender Dahlia Plants – Are Dahlia Flowers Annual Or Perennial
By: Mary H. Dyer, Credentialed Garden Writer
Are dahlia flowers annual or perennial? The flamboyant bloomers are classified as tender perennials, which means they may be annual or perennial, depending on your plant hardiness zone. Can dahlias be grown as perennials? The answer, again, depends on your climate. Read on to find out the real story.
Can Dahlias Be Grown as Perennials?
Perennials are plants that live for at least three years, while tender perennials won’t survive cold winters. Tender dahlia plants are actually tropical plants and they are perennial only if you live in USDA plant hardiness zone 8 or higher. If your hardiness zone is 7 or below, you have a choice: either grow dahlias as annuals or dig the tubers and store them until spring.
Growing Dahlias Year Round
In order to get the most of your dahlias, you’ll need to determine your hardiness zone. Once you know which zone you’re in, the following tips will help in growing or keeping these plants healthy and happy each year.
- Zone 10 and above – If you live in zone 10 or above, you can grow dahlia plants as perennials. The plants require no winter protection.
- Zone 8 and 9 – Watch for foliage to die back after the first killing frost in autumn. At this point, you can safely cut the dead foliage to 2 to 4 inches (5-10 cm.) above the ground. Protect the tubers by covering the ground with at least 3 or 4 inches (7.5-10 cm.) of bark chips, pine needles, straw or other mulch.
- Zone 7 and below – Trim the dahlia plant to a height of 2 to 4 inches (5-10 cm.) after frost has nipped and darkened the foliage. Dig clumps of tubers carefully with a spade or garden fork, then spread then in a single layer in a shady, frost-free location. Allow the tubers to dry for a few days, then brush off loose soil and trim the stems to about 2 inches (5 cm.). Store the tubers in a basket, paper bag, or cardboard box filled with moist sand, sawdust, peat moss, or vermiculite. (Never store the tubers in plastic, as they will rot.) Place the container in a cool, dry room where temperatures are consistently between 40 and 50 F. (4-10 C.).
Check the tubers occasionally throughout the winter months and mist them lightly if they begin to look shriveled. If any of the tubers develop soft spots or begin to rot, cut off the damaged area to prevent the rot from spreading to other tubers.
Note: Zone 7 tends to be a borderline zone when it comes to overwintering dahlias. If you live in zone 7b, dahlias may survive the winter with a very thick layer of mulch.
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Read more about Dahlia Flowers
How to Plant, Grow and Care for Dahlias
Available in thousands (really) of variations, dahlias bloom well into fall—and with just a little post-frost work, can survive for an encore come spring.
One of the world's most diverse flower species, dahlias dazzle from June or July until October.
Here's how to get the most out of the growing season.
1 Choose a spotDahlias grow best in moist, well-drained soil with full sun. Depending on the variety, they will reach between 1 and 8 feet tall.
2 Go shoppingSome growers sell plants, but for the best variety and prices, order tubers (similar to bulbs) at an online resource such as dahlias.com.
3 Plant the tubersWell after last frost (late May or early June), plant tubers and water them. Ideally, when plants emerge, mulch with 2 inches of hay or compost to keep roots cool.
4 Keep them tidyWhen plants reach 6 inches, remove all but the strongest stem. When plants reach 1 foot and have leaves, trim tops to encourage branching. Stake tall plants or use cages.
Great clips The more you harvest, the more dahlias bloom, so fill vases and deadhead often. Avoid cutting under midday sun.
Three steps to saving your dahlias for next year:
1 DigIn cold zones like the Midwest, dig up tubers a week or so after the first hard frost. Cut stalks to 5 inches. Let tubers dry one to two days out of the sun. Rinse and let dry fully. Label with a marker.
2 DivideDivide big clumps in half through the stalk. Place in a Styrofoam box or crate. Cover with vermiculite or a combo of newspaper and pine shavings. Store in a cool spot, such as a basement. (Check occasionally mist lightly if shriveling.)
3 Divide againIn spring, further divide clumps into small ones or individual tubers to make new plants. Make sure each cluster or tuber has an "eye," a bud on the knobby end that will sprout a stem.
How a handful of tubers crossed the Atlantic in a ship's hold and changed flower history. Centuries ago, a few species of dahlia grew wild in Mexico. (Aztecs used them for food and medicine.) In 1789, botanists sent dahlia tubers to the Royal Gardens of Madrid for scientific study. Two centuries of eager hybridization later, gardeners can choose from some 50,000 varieties-and they all descend from those original Mexican ancestors.
How to Grow Dahlias in California
Dahlias, tuberous perennials native to Mexico, are excellent flowers to grow in your California garden. They thrive in California's widely varied climates, which are spread through USDA Hardiness Zones 4 to 11. Although you can grow dahlias from seed and cuttings, the easiest way to grow them is from tubers. No matter which California climate you live in, plant your dahlia tubers in a location that receives at least six hours of sunlight each day.
Work 2 to 4 inches of compost or peat moss into the top 12 inches of soil. Also incorporate 2 to 4 lbs. of a balanced fertilizer (8-8-8 or 10-10-10) for every 100 square feet of planting space. Do this about six weeks prior to planting.
- Dahlias, tuberous perennials native to Mexico, are excellent flowers to grow in your California garden.
Select dahlias that grow well in your California climate, particularly in zones 9 to 11 where summers are extremely hot. There, choose varieties that can withstand the summer heat, such as the Prince Noir and Winsome. In cooler zones, most dahlias will grow well.
Plant your tubers directly outdoors after the last spring frost, which varies among the different California climates. If you live in an area where frost is not an issue, plant them anytime in the spring.
Loosen the soil to a depth of 12 inches and then plant your tubers on their sides about 6 inches beneath the soil with the eyes facing up. Fill the holes with 2 to 3 inches of soil and only fill in the rest as they grow. Exact spacing between tubers varies among the different varieties, but in general, about 2 to 4 feet apart will suffice.
- Select dahlias that grow well in your California climate, particularly in zones 9 to 11 where summers are extremely hot.
- Plant your tubers directly outdoors after the last spring frost, which varies among the different California climates.
Apply 3 to 4 inches of mulch such as bark or pine needles. During the hot California summer, be sure to add more mulch as it decays and settles.
Water your dahlias to keep the soil moist, usually about 1 inch of water a week. However, during the hot summer months in the coastal and southern portions of the state, you will most likely need to water them two or three times a week to keep the soil moist.
Thin the shoots as they grow, if desired. Each tuber can grow more than one stalk. To get the best blooms, clip off the extra shoots so all the plant’s energy will go into just one flowering stem.
- Apply 3 to 4 inches of mulch such as bark or pine needles.
- During the hot California summer, be sure to add more mulch as it decays and settles.
Insert a stake for tall dahlias once they reach about 12 inches tall or add the stake at planting. Place the flower stake next to the planting hole and loosely tie the stem to the plant with twine as the dahlias grow.
Fertilize dahlias in July with the 2 to 3 lbs. of 5-10-10 or 10-10-10 fertilizer. Follow the dosing instructions on the label for correct application methods. Water your dahlias well after fertilizing.
Cut the foliage in the fall after the first killing frost in USDA Hardiness Zones 4 to 7. Dig the tubers up and store them in damp perlite, vermiculite or peat moss in an area between 35 and 50 degrees Fahrenheit. In zones 8 and warmer, cut the foliage to about 2 to 4 inches and cover them with mulch during the winter months.
Broken, Shrivelled, and Dead Dahlia Tubers
No matter how well you try and store your dahlias over the winter, you will likely end up with some broken, shrivelled, mouldy, or dead dahlia tubers. Some can be salvaged, and others can’t.
Broken dahlia tubers are the best candidates for actually surviving. As long as they have an eye on them, they should bloom that year. If a tuber breaks, let it dry until it has a bit of a scab over the broken part, then try planting it in the spring.
Mouldy dahlias tubers are generally not worth planting, and will just eventually rot. Put all mouldy tubers into the compost.
Shrivelled dahlia tubers happen when the area you store them in is too warm. If the tuber feels papery and hollow, it has shrivelled too much and is dead. If is still has something to it, it can still possibly grow and thrive.
So that’s basically what you need to know to grow beautiful dahlias! Now head over to my post about overwintering dahlias, the best varieties to plant for cut flowers, and where to purchase dahlias.
Planting Dahlias in Your Vegetable Garden
One thing all dahlia lovers have in common is a shortage of growing space. No matter how big your garden is, there are always more must-have varieties than you have room for.
Last spring, I filled up my cutting garden and perennial beds with plants I had started in my greenhouse and still had 6 or 8 extra dahlias. I could have given them away, but they were varieties I hadn’t grown before and I really wanted to see them bloom. After wandering around the yard looking for possible planting spots, I thought… why not the vegetable garden?
Dahlias are energetic plants with big appetites and they are at their best when grown in rich, loamy soil with access to as much moisture and fertilizer as they want. I discovered that if you give them the same growing conditions as a tomato plant, they do amazing things!
Tomato cages work great for supporting plants in my cutting garden, so I used them here as well. In the spring, I wrapped fabric around the cages (as I do with my tomatoes) to protect them from wind and cool nights. Both are tropicals and love all the extra warmth they can get. Above is ‘Icoon‘ with its first flowers just starting to open.
Below is another picture of that same plant, taken from the opposite direction a few weeks later. The cage is now completely hidden by foliage and buds. On the left side against the fence is ‘H.S. Date‘, growing happily between lemongrass and oregano.
Below is a photo from mid-August. The tomato cages are still doing their job, keeping the plants nice and straight. Note that the flowers of Icoon are actually more orange than they appear here in early morning light.
‘Thomas Edison‘ (also shown in the first image in this blog post) wound up with the summer squash and pumpkins. Everyone is always impressed by the size of dinnerplate dahlias, and the plants easily held their own with those big-leaved vines.
I’ll leave you with one more photo from last year. ‘H.S. Date‘ is a single dahlia and I wasn’t sure I’d be a big fan. But I loved its dark foliage and the blossoms have long stems that are great for cutting. What sealed the deal was seeing how many bees and hummingbirds are drawn to the flowers.
From late summer through fall, I could look out my office window almost any time of day and see hummingbirds working their way around the plants. My camera doesn’t have a very powerful zoom lens, but if you look at the top flower that’s facing away from the camera, you can see one of those hummingbirds stopping by for a sip.
By keeping my vegetable garden a little tidier than usual and being more diligent with succession planting, I still had plenty of room for edibles. So I’m repeating the idea this year and adding some gladiolas , too. If you are looking for more places to be planting summer bulbs, consider feeding your passion by mixing them in with your vegetables!
Thanks for the tip. I have the same problem with Dahlias and my vegetable garden is pretty with dahlia blooms mixed in, I actually redesigned a perennial garden last fall so i could fit more dahlias this year.
I would caution against putting glads in your vegetable garden. They really spread and can be hard to get rid of (I’m in western Washington, it might be different in Vermont).
Thanks for the tip, Carol. Plants behave so differently in different climates. I treat glads as annuals, so in the early fall I use a garden fork to gently lift out the plants with corms attached. That way the little bublets around the corms stay attached and very few wind up staying in the bed.
Dahlias are tender annuals, but you can overwinter them pretty easily. In fall, after the first frost has blackened the foliage, cut off all but 2 to 4 inches of top growth, and carefully dig tubers without damaging them. Allow tubers to dry for a few days in a frost-free location, out of direct sunlight. Once dried, remove any excess soil, leaving 1 to 2 inches of stem. Store each clump of tubers in a ventilated box or basket. Fill the box with slightly moistened sand, peat moss or vermiculite and place it in a cool, dry location with temperatures that remain between 45 and 55 degrees F. Check tubers periodically through winter for rotting and drying out. If the tubers appear shriveled, mist them lightly with water. If any start to rot, trim the rotted portion of the clump so it won't spread. The tubers are fragile, so be careful when handling them.
When warm weather arrives, you can plant the overwintered tubers and begin the cycle again.